1. Field of the Invention
The present invention relates to corrosion inhibition. More particularly, the present invention relates to corrosion inhibition in aqueous systems. Still more particularly, the present invention relates to a composition and method for controlling corrosion of metal in aqueous systems.
2. Description of the Prior Art
Numerous chemical materials and combinations of materials have long been employed for inhibiting corrosion of metals in the aqueous cooling systems of industrial manufacturing processes, commercial and institutional air conditioning systems, steam generating systems, and the like. Included among such chemical materials are chromates, zinc salts, nitrites, silicates nitrates, polyphosphates and benzoates. More recently, organophosphonates have found increased use as mild steel corrosion inhibitors in aqueous systems because of their greater resistance to hydrolysis. As compared to polyphosphates, therefore, this renders them less prone to insoluble orthophosphate formation which tend to plug piping and affect the heat transfer surfaces of the systems in which they are employed. Organophosphonate inhibitors, moreover, are environmentally more acceptable than zinc salt and chromate inhibitors, both of which are effective but restrictive in use because of their toxicities. Examples of organophosphonates useful as corrosion inhibitors in aqueous systems are 2-hydroxyphosphonoacetic acid and aminoalkylenephosphonic acid derivatives in combination with a managanese compound as disclosed in U.S. Pat. Nos. 4,640,818 and 4,774,018.